1. Field of the Invention
The present invention relates to a method of manufacturing an optical waveguide for widespread use in optical communications, optical information processing, position sensors, and other general optics.
2. Description of the Related Art
In general, an optical waveguide is configured in such a manner that cores serving as a passageway for light are formed in a predetermined protruding pattern on an upper surface of an under cladding layer, and that an over cladding layer is formed so as to cover the cores. For the production of such an optical waveguide, the under cladding layer, the cores and the over cladding layer which are made of photosensitive resin compositions and the like as materials thereof are generally formed in a stacked manner in the order named on a substrate of stainless steel foil and the like by a photolithographic method and the like.
When the optical waveguide is used as a touch position sensor for a touch panel, there are cases where a light-emitting section and a light-receiving section in the over cladding layer are formed in a lens-shaped configuration. A mold is used to form the over cladding layer in a specific shape in this manner.
An exemplary method of manufacturing an optical waveguide using the aforementioned mold is as follows. First, a mold including a cavity having a mold surface complementary in shape to the surface of an over cladding layer is prepared as the aforementioned mold. Then, an under cladding layer and cores are formed in the order named on a substrate. Thereafter, a photosensitive resin composition, for example, for the formation of the over cladding layer is applied to cover the cores. Using the aforementioned mold, the applied coating layer is pressed into the shape of the over cladding layer. In that state, part of the molded coating layer is hardened to form the over cladding layer. Such a technique is disclosed, for example, in Japanese Published Patent Application No. 2008-203431. In another exemplary method, a mold including a through hole in communication with the aforementioned cavity is prepared as the aforementioned mold. The opening surface of the cavity of the mold is brought into intimate contact with the upper surface of the under cladding layer. In that state, a photosensitive resin composition, for example, for the formation of the over cladding layer is introduced through the through hole into the cavity, and is then hardened to form the over cladding layer. This technique is disclosed, for example, in Japanese Published Patent Application No. 2008-281654.
In these manufacturing methods, the positioning of the aforementioned mold is generally performed with respect to an alignment mark formed to protrude from the upper surface of the under cladding layer. The alignment mark is generally made of a material for the formation of the cores by a photolithographic method during the formation of the cores. For purposes of improving the positioning accuracy of the mold and reducing tact time, a CCD camera is used to automatically recognize the alignment mark.
However, even when the alignment mark is automatically recognized using a CCD camera so that the positioning of the mold is performed, there are cases where the alignment accuracy of the over cladding layer relative to the cores is lowered and the positioning of the mold is time-consuming. The lowered alignment accuracy of the over cladding layer relative to the cores reduces the intensity of light emitted from the light-emitting section in the over cladding layer. The use of such an optical waveguide as a touch position sensor for a touch panel causes the reduction in sensor performance. Also, the time-consuming positioning of the mold as mentioned above causes the reduction in productivity of optical waveguides.